1. Field of the Invention
This invention relates generally to rod lenses such as graded index (GRIN) lenses and more particularly to the coupling of light from waveguides to one or more lenses.
2. Background of the Invention
It is well known to couple light from one optical fibre to another through a pair of collimating lenses, for example graded index (GRIN) lenses. Furthermore, it is well known to couple light from one optical fibre to another through a single GRIN lens via a reflecting element on or near the end face of the lens. Lenses of this type are produced under the trade name xe2x80x9cSELFOCxe2x80x9d; the mark is registered in Japan and owned by the Nippon Sheet and Glass Co. Ltd. However, it is less well known, that substantial coupling losses may occur between an input port on a first GRIN lens, or other type of collimating lens and an output port an a second GRIN or other type of collimating lens, when the input and output ports are disposed adjacent the optical axes of the two collimating lenses, and when the distance or gap between the lenses is significant. One aspect of this invention addresses this problem and provides a solution to overcome or substantially reduce this unwanted coupling loss.
Although the detailed description hereafter concerns GRIN lenses, aspects of this invention are also relevant to the use of other types of collimating lenses and should not be limited to graded index lenses.
Substantial coupling losses may occur between an input port on a first GRIN lens and an output port and a second GRIN lens, when the input and output ports are disposed adjacent the optical axes of the two GRIN lenses, and wherein an optical element is disposed between the GRIN lenses wherein the element causes a beam propagating from the input port through the first GRIN lens to be shifted as it traverses the element towards the output port and enters the second lens at an offset to the optical axis of the lens.
As requirements for optical filters become more stringent, in some instances their thicknesses increase substantially. This increase in thickness increases the required gap between a pair of collimating lenses.
Typically, dichroic optical filter based devices are manufactured by disposing one or more filter layers between a pair of substantially quarter pitch GRIN lenses.
It is an object of this invention to overcome this disadvantage wherein a large gap is present between two collimating lenses, thereby causing a beam exiting a first collimating lens to enter a second adjacent collimating lens at a location at least partially shifted from its optical axis.
It is an object of this invention to overcome coupling losses normally associated with fibre to fibre GRIN lens systems wherein thick optical elements are disposed between a pair of GRIN lenses.
And, it is a further object of the invention to overcome coupling losses normally associated when an optical element disposed between a pair of GRIN causes a shift of a beam incident thereon.
Another significant advantage of this invention is that under conditions wherein a gap between lenses is not significantly large, and coupling losses are not of particular concern, cost savings are afforded by obviating the requirement to polish one or more GRIN lenses in an optical arrangement, for example in an optical filter.
Generally, GRIN lenses are polished at both ends with a slant complementing the slant of an adjacent fibre tube end containing optical fibres. Providing complementary slanted end faces between optical fibres and an adjacent lens lessens the effect of unwanted back reflections. In this arrangement a pair of GRIN lenses are disposed back-to-back having for example, a dichroic filter disposed therebetween. The inside faces of the lenses are often not polished with an angle, however outside faces adjacent the slanted end faces of the tube are generally polished with a slant. Typically, the lenses have coaxial longitudinal axes, and longitudinal axes of the optical fibre tubes are also coaxial with the axes of the rod GRIN lenses. This is shown in FIG. 13. Hence, the optical fibres contained within the tubes are typically parallel or in some instances coaxial with the optical axes of the lenses.
This invention provides an optical coupling arrangement wherein one or more GRIN lenses do not require a polished slanted end face adjacent an optical fibre tube. Obviating the requirement to polish the lens or at least an end face thereof, provides significant cost reduction in the manufacture of optical components.
In accordance with the invention there is provided, an optical coupling system comprising: a first substantially focusing/collimating rod lens having substantially parallel end faces orthogonal to a longitudinal axis;
a second substantially collimating/focusing rod lens having substantially parallel end faces orthogonal to a longitudinal axis;
an optical element disposed between the two rod lenses;
a first optical fibre tube adjacent to and optically coupled with at least one of the rod lenses, the optical fibre tube having a longitudinal axis which is non-parallel to the longitudinal axis of a rod lens adjacent thereto, a line extending along the longitudinal axis of the first optical fibre tube intersecting a line extending along a line extending along the longitudinal axis of the adjacent rod lens at a non-zero angle.
In accordance with the invention there is further provided, an optical coupling system comprising:
a first substantially focusing/collimating rod lens having at least one end face that is substantially orthogonal to a longitudinal axis of the rod lens;
an optical fibre tube adjacent to and optically coupled with the rod lens, the optical fibre tube having a longitudinal axis which is non-parallel to the longitudinal axis of a rod lens such that a line extending along the longitudinal axis of the optical fibre tube intersects a line extending along a line extending along the longitudinal axis of the adjacent rod lens at a non-zero angle.
In accordance with the invention, there is further provided, an optical coupling system comprising two GRIN lenses and two optical fibre tubes, each optical fibre tube having an end of an optical fibre therein, each optical fibre end being optically coupled and adjacent to an end face of a different one of the two GRIN lenses, at least one of the optical fibre tubes having a slanted end face facing one of the-GRIN lenses, the GRIN lens face facing the slanted end face of the tube, being non-slanted and orthogonal to a longitudinal axis of said rod lens.